Damp Bungalow

[Potatoman]

Hi I have a 85sq m Bungalow which is pretty well sealed up, so consequently got mould problems. Thinking about getting some window vents fitted and a PIV system, what does anybody think of these, whats a good make to get, should I get one with a heater in or not, are they expensive to run with a heater in. anything I have missed ?Thanks in advance

[JohnMo]

You can either suck air from the loft and blow out of room vents, or suck in through room vents and blow out of wet rooms. I prefer the later but either will work. PIV may be easier to install.

 

But either way I would want it humidity controlled to limit ventilation when possible. So fan humidity controlled and room vents the same. This way you only really ventilate where it's needed.

 

So if PIV, find one with humidity control of fan speed 

 

Or dMEV fans in wetrooms only, something like Greenwood CV2 or CV3.

[Iceverge]

Suck out of your can. 

 

Replacing bathroom fans with dMEV like John said is the easiest and cheapest. 

 

You probably have loft space for a centeralised MEV system or maybe even a MVHR if you want to go all in. 

[Potatoman]

Hi, been talking to Vent Axia about their centralised MEV system and they have said I need to get somebody to survey the bungalow  as you need to measure duct length and pressure build up, etc to get the correct system for the job, is this correct. Or is there a better way to tailor the system to the house.

[Potatoman]

Anybody?

[JohnMo]

Plenty of companies do MEV. You want one that automatically adjusts fan speed for humidity levels with extract vents that open and close automatically also. Then couple that with humidity activated inlet vents either in window or through wall.

 

Do some reading via Google 

Passivent, Deco, to name a couple.

 

You need to have air movement with cross ventilation dry areas to wet and out the house. To allow this you also need door under cuts or through wall vent grills.

 

I would keep it simple and do dMEV, with all the features mentioned above.

[marshian]

On 13/01/2026 at 19:51, Potatoman said:

Hi I have a 85sq m Bungalow which is pretty well sealed up, so consequently got mould problems. Thinking about getting some window vents fitted and a PIV system, what does anybody think of these, whats a good make to get, should I get one with a heater in or not, are they expensive to run with a heater in. anything I have missed ?Thanks in advance

 

I fitted a PIV unit centrally in the house (4 bed over two floors) as a result of humidity levels spiking after I insulated under my suspended ground floor (great idea from a heat loss perspective but it had clearly been a major contributor of uncontrolled air ingress)

 

Within a few days the PIV unit had brought the house into a level of control initially on a higher flow setting but now it's on a timed schedule (midnight to 6.00 am and 8.30 am to 3.00 pm as this works for our occupancy routine.

 

I did buy one with a heater but 400W consumption can rapidly increase electricity usage when it cuts in so I've got it turned off.

 

I do have trickle vents in a few windows (not all because most predate the requirement) but a fair percentage of the air pushed into the house is ventilated out via bathrooms fan extracts even when the fans are off. (this is exactly what I need as dry air expels the warm wet air in bathrooms)

 

Overall it works well for us 

 

 

[Mike]

On 13/01/2026 at 20:51, Potatoman said:

PIV system, what does anybody think of these

There's best avoided - the problem is that they tend to push moisture-laiden internal air through gaps in the building, leading to condensation within the structure.

 

MEV avoids this risk. Choose either a central central unit, or decentralised dMEV.

 

On 16/01/2026 at 21:45, Potatoman said:

I need to get somebody to survey the bungalow  as you need to measure duct length and pressure build up, etc to get the correct system for the job, is this correct. Or is there a better way to tailor the system to the house.

If you're not going to DIY it, then yes, you need to find a contractor to propose a solution. You can post their proposal here for feedback.